Primary angle closure glaucoma is a significant cause of visual loss and blindness. Appropriate therapy, however, when administered in time is highly effective in curing the disease and preventing loss of vision. It is also a disease that usually occurs acutely with little or no previous warning. Research to data has done little to provide indicators that might accurately identify eyes at risk so that appropriate treatment could be instituted prior to the onset of an acute (potentially blinding) attack. Recognizing these facts, the National Advisory Eye Council Vision Research Program Planning Committee indicated an urgent need for the study of early detection and treatment of angle closure glaucoma patients. The present project is designed as a two center coordinated study to determine the natural history of angle closure suspect patients. These patients will be subjected to an initial examination that will include a physiologic angle closure provocative test (the darkroom prone test), measurement of the anterior chamber depth by pachometry and determination of the axial length by the use of ultrasonic technique. The patients will then be followed expectantly for five years. It is expected that we will be able to more clearly determine the attack rate in this population and determine whether there are any correlations between the results of the provocative test or the biometric parameters and the subsequent incidence of acute attacks. This information could then provide the hard data that are needed to indicate whether specific Clinical Trials or other studies are indicated or justified.